Crows can be craftsman, too

Thinkers as diverse as Freud, Engels and Thomas Carlyle once pointed to the use of tools as being a defining behaviour of human beings. Then it was found that many animals also used them, from the "fishing sticks" of apes to the rocks dropped on ostrich eggs by Egyptian vultures.

Crows are particularly crafty. Earlier studies showed that they are almost human-like in their use of tools, with technological features that match the stone and bone tool cultures that emerged among primitive humans between 2.5 million and 70,000 BC.

But the anthropocentric still took solace from the fact that only humans were thought to have the brain power required for cumulative technological evolution. This is the skill for innovation that took our ancestors two million years ago from creating flakes of flint, for use in cutting, to honing knives, blades, arrowheads and axeheads.

Now this "unique" attribute of humans has also turned out to be a flattering delusion. A new study shows that the crows of New Caledonia are inventive. With their evolving leaf tools, the birds have levered man off his pedestal.

The creative skills of the birds are described this month in the Proceedings of the Royal Society by Dr Gavin Hunt and Dr Russell Gray of the University of Auckland. They have spent the past decade studying feathered technology in the islands of Grande Terre and Mare in the South Pacific archipelago of New Caledonia, 900 miles north-east of Australia.

After an intensive field survey of local crow industry - sampling 21 sites and 5,550 leaf tools - the scientists found that the birds rip the barbed leaves of the pandanus (screw pine) tree to fashion three distinct types of tool for grub and insect extraction: wide, narrow and stepped.

Because the strap-like leaves are reinforced by tough parallel fibres, the latter, tapered, design is best made in steps. With precision beak work, the crow nips the leaf, then rips along the fibres. Next it makes another cut and tears again, repeating until it has a tool with usually two, three or four steps.

The scars on the remains of leaves used by the crows revealed similarities in the cutting and ripping used for each of the three basic tool designs, and their different but overlapping geographic distributions. All the designs are found around Rivière Bleue, at the end of Grand Terre, suggesting the first, prototype, leaf tool was invented there to winkle bugs out of crannies.

It seems that being a crow is no bar to invention. Long ago, the birds discovered that they could rip the serrated edge off the leaves to make a wide tool. The skill spread and the crows honed tools with finer working tips by either narrowing tools or tapering them by creating stepped versions.

Leaf tool manufacture is probably an example of culture, one as real as art, literature or the opera: just as songs are passed down, so the birds learn through example and their tool-making wisdom grows in sophistication down the generations.

The crows appear to have the cognitive requirements for cumulative, though rudimentary, technological evolution, said Dr Gray. "Tool manufacture in New Caledonian crows show striking flexibility and innovation."

The ability of the birds to innovate is further shown by their making of other tools, such as hooks, and how they do not rely on one raw material: as well as pandanus, the birds make hooks out of twigs and similar materials.

They often strip a twig of leaves, and sometimes of bark, and cut it off just below a shortened offshoot to create a hook to weedle out bugs. They also use simpler tools to extract the grubs of wood-boring longhorn beetles from the dead wood of candlenut trees.

The crows even work like human artisans who shape tools according to a set pattern with a favoured hand - the birds use the same routine of cuts and rips, preferring to use the left edge of the leaves and probably their right eyes.

Prof Alex Kacelnik, fellow of Pembroke College, Oxford, praised the study as "extremely important". It complements his own research, with Dr Jackie Chappell and Alex Weir, which has turned Betty the New Caledonian crow into a star by revealing her to be the first animal, other than man, to show a basic understanding of cause and effect.

Betty began making tools after her partner, an old male called Abel (now deceased), snatched away a hook made for her by the researchers, forcing her to make her own from garden wire to fish out morsels from a tube.

She wedged the end of the wire into the base of the food tube and turned her head to form the hook. What amazed the researchers is that she can even adapt her hooks if they are not up to the job, something that even chimpanzees are unable to do. Although chimps use sticks in experiments they have not shown any human-like understanding of basic physical laws.

"She shows from the start that when she starts bending the wire it is as if she has a clear objective, even correcting the angle of the hook if it is not right," said Prof Kacelnik. "Although many animals use tools, purposeful modification of objects to solve new problems, without training or prior experience, is virtually unknown."

Not all crows are so creative. Abel found an easier solution to the problem of finding food: he stole Betty's after she had hooked it out.

By human standards, New Caledonian crows are no birdbrains: our ancestors only cottoned on to the idea of hooks some 80,000 years ago. And children don't realise what a hook can do until they are two or three years old.

"While we have been emphasising the invididual ability of animals like Betty to solve problems, the New Zealand team has been emphasising tool manufacture, the cultural traditions and transmission of information in the wild," said Prof Kacelnik.

Both strands of research are related by how the crows are not genetically programmed to use a tool, like a spider and his web. Instead, the birds creatively invent new kinds of tools to solve problems and can share skills with others.

Corvids - the crow family - are the Einsteins of the Avian world, though Prof Kacelnik added that, at least in terms of tool making, the Pacific crows are smarter than their British cousins and their skills have even been celebrated by the issue of a New Caledonian stamp.

Perhaps their natural talent arose from their astonishing beak dexterity. "We have not yet identified what it is that makes these crows so special, though it is something to do with the ecological circumstances on the island,'' said Prof Kacelnik.

The question of what's going on in a crow's mind will take much time to answer. Once scientists have got to the bottom of what makes Pacific crows master toolmakers, they may have to think again about how this skill evolved in humans.

27 march 2003